1. Field of the Invention
This invention relates to a system of electrically making automatic adjustment of the blackening degree of an X-ray photograph obtained by X-ray photograph.
2. Prior Art
The quality of an X-ray photograph obtained by an X-ray phtographing apparatus depends upon the good or bad balance between the individual conditions of a person to be photographed, the tube current, and the tube voltage of an X-ray tube. This good or bad balance is judged by the blackening degree of the X-ray photograph. Particularly, in X-ray photographing in dental treatment, there is provided a variation in the dose of X-rays which reach the surface of the film because of differences between adults and children, between sexes and between front teeth, false teeth and true molars even if the teeth are those of the same person to be photographed. Even though a good contrast is obtained in certain parts of the film, it happens that a good contrast cannot be obtained in other parts because of wide deviation of the film in blackening degree from an optimum value. In the prior art, to solve this problem, the illuminance has been adjusted by adjusting the tube voltage. This is not an advantageous method because the change in voltage by such adjustment provides a change in wave length of the X-rays, particularly when the tube voltage is lowered and as the wave length is increased the X-rays are absorbed by the soft part of the patient's mouth region.